The present invention relates to apparatus for restoring distorted articles, such as containers, which are of nominally circular cross-section, to their true circular cross-sectional shape. Particularly, the invention relates to apparatus for successively advancing distortable articles of nominally circular cross-section through a processing station and at least temporarily restoring each distorted article to its circular cross-sectional shape whilst a predetermined operation is performed in connection with the article as it is advanced through the station. More particularly, although not exclusively, it relates to apparatus for ensuring that distortable containers of nominally circular cross-section are of true circular cross-sectional shape as they are advanced through a station at which closures are applied to the mouths of the containers.
Cylindrical or frusto-conical containers having outwardly directed flanges or rolled beads about the mouths of the containers are frequently closed by the application to the mouth of each container of a closure cap made from metal foil. Such a cap is provided with a shallow cylindrical skirt having an internal diameter slightly greater than the external diameter of the mouth of the container. The lower portion of the skirt may be mechanically crimped or swaged under the flange or rolled bead about the mouth of the container to secure the cap in position. Additionally, the cap may be heat-sealed to the rim of the container mouth by providing the metal foil from which the cap is made with a coating of thermoplastic resin adhesive or a plastics film compatible with the container material and applying heat and pressure to the cap, when located on the container mouth, by means of a heated platen. This type of container/closure combination is widely used in the dairy industry for packaging products, such as yoghurt and cream, and for these products, the container is made by vacuum-forming or injection moulding thermoplastics material, such as, polystyrene or polypropylene. The external diameter of the mouths of such containers can be maintained to close tolerances and the mouth will retain its circular shape after manufacture and during storage and transportation to the packaging plant. Therefore, caps can be reliably applied to such containers by automatic machinery and only require a slightly greater diameter than the container mouth to ensure correct, distortion-free application. A typical clearance between cap and container diameters is of the order of from 0.010 inches to 0.020 inches.
The economy and easy-of-opening characteristics of foil caps make these attractive for use with other types of containers, such as, those manufactured from various laminated combinations of paper board, aluminium foil and thermoplastics film. For example, one type of cylindrical container body is produced by wrapping a rectangular piece of laminated material about a cylindrical mandrel and sealing the overlapped edges with adhesive or by firmly welding plastic films on each side of the laminate. Alternatively, cylindrical container bodies may be manufactured by spirally winding one or more continuous lengths of a suitable laminate material on a cylindrical mandrel and thereafter cutting the resulting tube into container bodies of the required length. In either event, the end of the container body which will form the mouth of the container to be subsequently sealed by a metal foil cap, may be reinforced by rolling an outwardly turned bead about this end of the container body.
Containers made from laminate material by either of the above methods are dimensionally unstable and readily become distorted from their true circular cross-sectional shapes. This can cause considerable problems and unreliable or defective application of closures when thin foil caps are applied by automatic machinery.
Hence, there is a need for apparatus which will ensure that cylindrical or frusto-conical containers made from laminate material are of truly circular cross-sectional shape when they are fed through automatic capping machinery and which will restore distorted containers to their nominal shape, at least temporarily, whilst the caps are being applied.